Solar cells currently used can be classified into various types according to light absorption layer material and intended use. Especially, organic solar cells, which contain organic compounds having an electron donating function and an electron accepting function and placed between two different types of electrodes, are attracting attention because they can be manufactured by processes simpler than those for inorganic solar cells, typified by silicon solar cells, can be made to have a larger area at low cost, and can be made colored or flexible.
Organic solar cells generally utilized include dye-sensitized solar cells, which use organic dyes to generate electromotive force, and organic thin-film solar cells, which use organic semiconductors.
To put the organic solar cells into practical use, it is necessary to increase their output voltage. Thus, organic solar cell modules have been developed, which have a plurality of connected organic solar cells.
Concerning methods for manufacturing the organic solar cell modules, for example, Patent Literatures 1 and 2 disclose the following manufacturing methods.
For example, Patent Literature 1 discloses a method for manufacturing an organic thin-film solar cell module, which comprises steps of: forming a first conductive layer and a photoelectric conversion layer in a pattern on a support, forming a second conductive layer and a carrier transport layer in a pattern on a flexible film, and bonding the support and the flexible film together in such a manner that the photoelectric conversion layer and the carrier transport layer are in contact with each other and the first and second conductive layers are partially in contact with each other to be connected in series.
Unfortunately, this manufacturing method has the problem of complicated process because in this method, each layer must be patterned in forming the organic solar cell module.
For example, Patent Literature 2 discloses a method for manufacturing a dye-sensitized solar cell module, which comprises steps of: making a plurality of dye-sensitized solar cells by forming each solid electrolyte layer on each oxide semiconductor electrode substrate having an electrode substrate and a sensitizing dye-bearing porous layer and by bonding each solid electrolyte layer to each counter electrode substrate having a counter electrode layer; and connecting these solar cells to form a dye-sensitized solar cell module.
Unfortunately, this manufacturing method has the problem of involving a large number of steps because the method includes steps of making a plurality of dye-sensitized solar cells, respectively, and steps of connecting dye-sensitized solar cells to each other.
In addition, the dye-sensitized solar cell module manufactured by this method also has the problem that its strength can be insufficient because the dye-sensitized solar cells are individually formed and connected.
Patent Literature 3 discloses a method for manufacturing a dye-sensitized solar cell, which comprises steps of: forming a partition wall layer around the porous layer of the oxide semiconductor electrode substrate mentioned above, applying a pseudo-solid electrolyte to the inside of the partition wall layer, in which the pseudo-solid electrolyte contains a conductive carbon material and a solvent, then removing the solvent to form a pseudo-solid electrolyte layer, and boding the product to the counter electrode substrate to form a dye-sensitized solar cell.
Patent Literatures 4 and 5 respectively discloses a method for manufacturing a dye-sensitized solar cell, which comprises steps of: forming a partition wall part on the counter electrode substrate mentioned above, forming a gel electrolyte layer inside the partition wall part, and then bonding the product to the oxide semiconductor electrode substrate to form a dye-sensitized solar cell.
Unfortunately, the dye-sensitized solar cell-manufacturing methods disclosed in Patent Literatures 3, 4, and 5 have the following problem. If these methods are used to form a dye-sensitized solar cell module, the step of forming the partition wall layers or partition wall parts must be performed, and the counter electrode substrates and the oxide semiconductor electrode substrates must be aligned with high accuracy, so that the manufacturing process will be complicated.
These conventional methods for manufacturing an organic solar cell module all involve a complicated process. Thus, there has been a demand for a method that makes it possible to manufacture an organic solar cell module with higher productivity.
On the other hand, organic solar cell modules are required to have a highly flexible structure so that they can have higher workability.
For example, a conventional flexible organic solar cell module includes a plurality of organic solar cells formed between two flexible substrates.
Unfortunately, such a conventional module has the following problem. If the organic solar cell module having the above structure is bent, the two flexible substrates will have different curvatures, so that it may be difficult to provide the desired bending properties or the organic solar cell module may be damaged by the bending.
Thus, Patent Literature 6 discloses a method for manufacturing a dye-sensitized solar cell module, which comprises steps of: providing a first electrode substrate including a single first substrate and a plurality of first electrode layers formed thereon, providing a plurality of second electrode substrates each having a second electrode layer, arranging the first electrode substrate and the second electrode substrates in such a manner that the plurality of first electrode layers formed on the single first electrode substrate are each opposed to the second electrode layer of the second electrode substrate, bonding the first and second electrode layers together with a sealing agent or an adhesive interposed therebetween, and then injecting an electrolyte between them. This method makes it possible to obtain a highly flexible dye-sensitized solar cell module because in this method, a plurality of first electrode layers are formed on a single first electrode substrate, and each second electrode layer formed on each second electrode substrate can be placed opposite to each first electrode layer on the substrate to form a dye-sensitized solar cell module.
Unfortunately, this manufacturing method has the following problems. In this method, the step of injecting an electrolyte must be performed after the first and second electrode substrates are bonded together, so that it takes a long time to form a large-area cell. In this method, adhesion parts, insulating parts, and other parts must be formed to bond the first and second electrode substrates together, and such adhesion parts, insulating parts, and other parts cannot contribute to power generation in the dye-sensitized solar cell module, which will reduce the total power generation area of the dye-sensitized solar cell module and lower its power generation efficiency and may lead to excessive use of materials such as substrates.
Incidentally, there has been found no manufacturing method capable of forming an organic thin-film solar cell module with good flexibility.